1. Not standing still
Football is a game of inches; pool is a game of millimeters. In a game where precision is absolutely necessary, you must remain as still as possible. There’s a reason why surgeon’s have hands that are notoriously still, just imagine what it would be like if their whole bodies were swaying. I do know some players with Parkinson’s, and pool is extra challenging for them, but in general think “statue” before you shoot.
2. Jerking up after your shot
But you say, I already hit the ball, what difference does it make? If you remain perfectly still throughout your delivery, then none. But more often then not, this is not the case. If you do lift up, when the pressure comes, this will be even more exaggerated then it was before. Do yourself a favor and stay down, not only will you play better, but you will look better too. If you really can’t stop, have someone hold a stick over your head so you can feel the problem.